1. Field of the Invention
The present invention relates to a chemical conversion treatment technique, and more specifically, to a chemical conversion treatment technique for forming a conversion layer on a surface of zinc or zinc alloy.
2. Description of the Related Art
A chromate treatment is a classical chemical conversion treatment for preventing a surface of zinc or zinc alloy from rust. The chromate treatment has been widely used in industry due to low cost and easy-to-use.
However, since hexavalent chromium is a hazardous substance, a restriction on its use is becoming more widespread. For this reason, studies on a chemical conversion treatment using trivalent chromium instead of hexavalent chromium and a chromium-free chemical conversion treatment are carried out vigorously.
For example, Jpn. Pat. Appln. KOKAI Publication No. 11-181578 describes a chemical conversion treatment liquid containing aluminum, silicon and one or more of organic acids or inorganic acids. This patent document also describes that addition of fluorine into the chemical conversion treatment liquid makes it possible to obtain an excellent appearance.
Jpn. Pat. Appln. KOKAI Publication No. 2007-177304 describes a chemical conversion treatment liquid containing at least one of a water-soluble inorganic salt of magnesium and a water-soluble inorganic salt of lithium; another water-soluble inorganic salt or a inorganic silicate or colloidal silica; and hydrogen peroxide. This patent document also describes that using the chemical conversion treatment liquid makes it possible to form a chromium-free layer having a sufficient corrosion resistance.